Effect of Ar, O₂, and N₂ Plasma on the Growth and Composition of Vanadium Oxide Nanostructured Thin Films

Abstract

Vanadium oxide nanostructured thin films (NTFs) are synthesized using plasma assisted sublimation process (PASP) in different gases' Ar, O2, and N2 plasma (AP, OP, and NP) and O2 gas (OG) ambient. Morphological studies conducted via electron microscopy reveal nanostrips, nanoflakes, nanorods, and nanoparticles organized as clusters for OP, OG, AP, and NP respectively. X‐ray photoelectron spectroscopy (XPS) studies show that samples OP and OG are composed of α‐V2O5, whereas AP and NP are composed of V6O13 along with V2O5. The relative percentages calculated using XPS data show that in AP, V6O13, and V2O5 are 38 and 62%, respectively. These percentages change to 48% for V6O13 and 52% for V2O5 in NP. The V6O13/V2O5 ratio is lower in AP than NP. This increment of V6O13 in NP is due to presence of more reductive species in N2 plasma than Ar plasma. Since N2 plasma contains species like N*, , etc. it leads to the formation of NO2, N2O, etc. Raman spectra indicate the surface of the sample NP consisting of both V6O13 and V2O5, agreeing with the X‐ray diffraction (XRD) and XPS results. Studies demonstrate that plasma ambient during synthesis process affects both morphology and composition of deposited vanadium oxide NTFs.

The Role of V‐Species and O‐Species on Controlled‐Hydrogen‐Reduction VOx Surfaces in Cyclohexane Oxidation

“…The Raman spectra indicating different vanado‐oxygen stretching vibrational modes which belongs to different vanado‐oxygen binding modes, V= T O bond, V− di−L O bond and V− tri−L O bond, described CHR‐VO x surface structural changes in the hydrogen reduction treatment, as shown in Figure 5(a). Nine peaks at 144 (B 1g /B 3g ), 195 (A g /B 2g ), 283 (B 1g /B 3g ), 301 (A g ), 403 (A g ), 483 (A g ), 523 (A g ), 701 (B 1g /B 3g ), and 993 (A g ) cm −1 confirm the different vanado‐oxygen stretching vibrational modes according to previous literature [14e,19] . The highest frequency peak at 993 cm −1 appeared due to the stretching vibrational mode of the V= T O bond alone in the Z direction.…”

Reactive Oxidation Induced Stoichiometric Modulation of Multivalent Vanadium Oxides

“…Raman spectroscopy is used widely to determine the phases of vanadium oxides because distinct Raman modes are exhibited depending on the vanadium oxidation state. [23,33] For example, V 2 O 3 with corundum structure has seven Raman-active modes (2 A 1g mode: 240 and 510; 5 E g mode: 218, 300, 378, 340, and 600 cm À1 ). [33] Monoclinic VO 2 showed 18 Raman-active modes (9 A g : 137, 194, 224, 310, 340, 393, 499, 612, and 633 cm À1 ; 9 B g : 143, 224, 262, 393, 442, 484, 582, and 820 cm À1 ).…”

“…[31,35] V 2 O 5 with an orthorhombic layered structure shows 8 Raman-active modes (4 A g : 194, 302, 406, and 526 cm À1 and 4 B g :143, 284, 697, and 707 cm À1 ). [23] Among them, the Raman peak around 143 cm À1 was derived from the layered structure of V 2 O 5 . [23] The as-grown film showed Raman mode at 752 cm À1 (*) derived from the c-Al 2 O 3 substrate, [36,37] and the weak Raman mode (♦) from a corundum structure V 2 O 3 at 200 cm À1 (E g mode) and 250 cm À1 (A 1g mode), as shown in Figure S4, Supporting Information, respectively.…”

“…[23] Among them, the Raman peak around 143 cm À1 was derived from the layered structure of V 2 O 5 . [23] The as-grown film showed Raman mode at 752 cm À1 (*) derived from the c-Al 2 O 3 substrate, [36,37] and the weak Raman mode (♦) from a corundum structure V 2 O 3 at 200 cm À1 (E g mode) and 250 cm À1 (A 1g mode), as shown in Figure S4, Supporting Information, respectively. The Raman modes of the monoclinic VO 2 (•) appeared for the film treated for 1 min.…”

“…Alternatively, O 2 plasma with higher reactivity has been used to enhance the oxygen reactivity and tune the vanadium oxidation state under ≈500 °C for ≈30 min. [21][22][23] Nevertheless, oxygen plasma treatment causes damage to the sample surface due to the direct bombardment of ions. Furthermore, the formation of an unexpected V 2 O 5 phase by the high reactivity weakens the phase controllability of films.…”